A conventional position measurement system 100 is shown in FIG. 1A. The system 100 includes a sensor 10, a pulse generator 20, and a signal receiver 24. The sensor 10 includes a waveguide 12 and a magnet 14. Such a position measurement system is described in greater detail in European Patent Application No. 12006827.5, filed Oct. 1, 2012, which application is incorporated herein by reference in its entirety. In general, the magnet 14 is attached to a moveable object. During operation, the pulse generator 20 generates a pulse 21 that is communicated to the waveguide 12. The magnet 14 creates an impedance discontinuity 11 in a region of the waveguide 12 proximate to the magnet 14. A reflection of the pulse 21 is reflected from the point of impedance discontinuity 11, resulting in reflected pulse 23. The signal receiver 24 receives the pulse 21 and the reflected pulse 23. The position of the magnet 14 relative to the waveguide 12 can be determined based on the timing of the pulse 21 with respect to the reflected pulse 23. More specifically, the difference between the time the pulse 21 is received and the time the reflected pulse 23 is received can be used to determine the position of the magnet 14.
The waveguide 12, however, is often temperature dependent. Said differently, the timing between receipt of the pulse 21 and receipt of the reflected pulse 23 may be dependent on temperature in addition to the position of the magnet 14. More specifically, temperature may affect the permittivity, capacitance, permeability, and/or inductance of the waveguide 12. Accordingly, the velocity of waves transmitted through the waveguide 12 may change; thereby changing the speed in which the pulse 21 and the reflected pulse 23 travel through the waveguide 12. Correspondingly, the time of receipt of the reflected pulse 23 may differ even when the point of discontinuity 11 is the same. For example, FIG. 1B shows a timing diagram 101. The timing diagram 101 shows a first pulse 21-1 and a second pulse 21-2. First and second reflected pulses 23-1 and 23-2 corresponding to the first and second pulses 21-1 and 21-2 respectively are also shown. The first and second reflected pulses 23-1 and 23-2 are reflected from the point of discontinuity 11 shown in FIG. 1A. In particular, the position of the magnet 14 is the same for both reflected pulses 23-1, 23-2. However, due to changes in temperature, the time 103 (Td1) between the first pulse 21-1 and the first reflected pulse 23-1 is different than the time 105 (Td2) between the second pulse 21-2 and the second reflected pulse 23-2.
Conventionally, position sensors attempt to compensate for temperature by using look-up tables, or the like. However, this requires additional circuitry to measure the ambient temperature, additional memory to store the lookup table, and additional processing capability to determine the actual position based on the look-up table. Furthermore, any inaccuracy or difference between the temperature data in the lookup table and the actual temperature dependence of the waveguide 12 will result in position measurement errors.
Furthermore, the propagation velocity of waves in a waveguide may be affected by other factors in addition to temperature. For example, the propagation velocity may change over the lifetime of the waveguide. The propagation velocity may be affected by external magnetic fields. Additionally, the propagation velocity may be affected by manufacturing tolerances.
It is with respect to the above that the present disclosure is provided.